The need to be responsive to market demand requires a greater emphasis on quality assessment resulting in the greatest need for grading of any agricultural produce as it procures high price to the grower and improves packaging, handling and brings an overall improvement in the marketing system. Today, the grading process has been fully mechanized. A mechanical grader consists of a chain conveyor belt, with a bag at the end along with fewer or more modifications like use of color sensors or use of image processing systems, etc. In grading machine, the grading machine grades smaller or bigger produce fall through the chain, making the grading process easier. Conventionally, the sorting machines provide a binary output. The objects are dumped from the hopper and they are made to slide on a set of channels. They present themselves to the cameras during the fall and the cameras decide upon the defects and if found any, then they actuate the ejectors and a high jet of air is passed for a short period of time making the desired object to fall into the collecting bin, thereby grading objects. During this process, when the object once made to fall and pass the camera, the accurate position of the object is not known so it becomes tedious to know the position of the object in real time and eject them into different grades based on their different properties. The conventional sorting machine need multi passes to get multiple distinguishable grades.
Few patent documents which describe sorting or grading of different objects as described hereinafter. U.S. Pat. No. 3,650,397 titled “system for inspecting and classifying objects such as screws, bolts and the like while in motion” discloses a system for sorting threaded objects such as screws, bolts comprising sequential detection. Disadvantage of the system can be observed as it sorts only the threaded objects and sorting is binary. The system further does not claim anything on the positioning of objects in the free fall. U.S. Pat. No. 3,773,172 titled “blueberry sorter” discloses an automatic sorting apparatus for object with an ejection system comprising a plurality of air nozzles disposed adjacent the carrier or input conveyor means and connected through high pressure air valves to a source of pressurized air. A logic network interprets the signals from the electronic system to cause selected air valves to be actuated at particular times so that air blasts, then pass through the apertures in the fruit laden cups to eject the fruit from the input conveyor means at different sorting stations onto output conveyors in accordance with the sensed condition of the fruit. The disclosed sorting machine is complex in arrangement and it is mainly designed to sort blueberries and other fruits such as apples, oranges, cranberries, grapes, cherries, and any other fruit or vegetables which have an approximately spherical shape, thereby limiting the scope of sorting by excluding other objects which are not fruits or vegetables. U.S. Pat. No. 6,814,211 titled “slide for sorting machine” discloses a slide for gravity sorting of objects. It uses a sensor to interpret the position of objects and according to its delay time uses an ejector to eject the object into a bin. The machine uses a delay time for ejection which may change due to different factors as it is an open loop system which leads to inaccuracy and inefficiency of the system while sorting objects. U.S. Pat. No. 7,905,357 titled “product flow control apparatus for sorting” discloses a feed control apparatus for use in a gravity slide sorter for sorting of products comprising an ejector system for sorting small objects such as almonds, peanuts and rice grains or other food or fungible materials. It eliminates particulate matter by detecting and ejecting objects falling from slant surface. A major disadvantage of the system is that it sorts the objects in acceptable and unacceptable (binary) items only. U.S. Pat. Application No. 20100096300 titled “chutes for sorting and inspection apparatus” discloses different sections of slant surfaces to gravity sort the objects in acceptable and unacceptable items. One of the disadvantages of the apparatus may be seen as the product pieces may get stuck due to alignments in slant sections, which will affect its accuracy. Another disadvantage is that the device sorts the objects in a binary fashion as acceptable and unacceptable classes only.
PCT Publication No. WO2016000967 titled “Transport apparatus with vacuum belt” discloses a system for sorting particles like grains, seed in three quality classes. It uses a vacuum belt to carry the particles from hopper at the lower end to the fixed camera at the upper end. A significant loophole of the system is blockage of the perforations on the vacuum belt due to foreign particles often associated with grain or seed, thereby decreasing its efficiency. Moreover, though the system sorts the particles in three quality classes, there is still tremendous scope ahead to explore in this area to provide multiple quality classes rather than only two or three classes or grades.
Typical sorting or grading systems that are known in practice, often less efficient due to limitation in the number of classes or grades that the machine provides and the lack of co-ordination in between tracking of accurate position of moving object and the actuation of ejectors to blast that object of particular characteristics to get quality grade without missing a single quality grade.
Therefore, there creates a strong need to solve above mentioned problems by providing a novel grading machine which is simple, more efficient, more accurate and cost-effective grading machine to grade different types of objects into multiple commercial grades in a single pass by continuously tracking their trajectory. It would also be desirable to provide a novel process for grading such objects into multiple commercial grades in an easy, simple and time-efficient manner.